(1) Big spangle
Spangles with a diameter greater than 3mm that can be distinguished by the naked eye are called large spangles, and some are also called normal spangles or natural spangles. The internationally recognized best size is 8~12mm.
In nature, lead and zinc are symbiotic deposits. When pyrometallurgical smelting is used, the density of the lead liquid is higher at the lower part, and the density of the zinc liquid is lower at the upper part, which can be separated. But the saturation concentration of lead in the zinc solution is 2%, so there is a large amount of lead in the crude zinc. Hot-dip galvanizing has a history of more than 150 years. At that time, there was no modern refining technology. Only crude zinc was used for hot-dip galvanizing. As lead is mixed in the zinc solution, hot-dip galvanized sheets must have spangles. Therefore, for a long time, it has been formed that hot-dip galvanized sheets must have spangles, and there is no wrong view that hot-dip galvanized sheets do not have spangles. The actual hot-dip galvanized sheet with spangles does not have any benefits: first, the zinc layer contains lead or antimony will accelerate the electrochemical corrosion rate, and reduce the service life of the hot-dip galvanized sheet by 15%-20%; second, there are spangles It will make the board surface uneven; third, the spangle is not conducive to further coating, because a spangle will appear a dark spot, but affect the appearance. At present, developed countries in Europe and the United States have not seen large spangle hot-dip galvanized sheets, and all have moved towards spangle-free products. Only the underdeveloped countries in Southeast Asia still retain large spangle varieties.
(Two) small spangles
Spangles with a diameter of 1~2mm are called small spangles. When the hot-dip galvanized sheet comes out of the zinc pot and sprays water mist or zinc powder on the unsolidified zinc layer, a water mist drop and a zinc powder particle will form a crystal center, which increases the number of spangles per unit area. Smaller, so the galvanized sheet surface will form small spangles that can be distinguished by the naked eye. Traditionally, the products produced by this process are called small spangles. Because this process often causes uneven spangles, uneven surface color, and high production costs, this process is currently not widely used.
(3) No spangles
Spangles cannot be seen with the naked eye on the board surface, which is called zinc-free or zero-spangled. This is done by controlling the chemical composition of zinc liquid. When hot-dip galvanizing, only a certain amount of aluminum is added to the zinc solution, and no lead, antimony, or tin is added to produce spangle-free products. This process does not increase equipment, does not increase production costs, and can obtain a uniform surface appearance, so this process has been widely promoted and applied all over the world.
(4) Smooth spangle
Large spangles are not allowed to enter the finishing process. After small spangle or non-spangle products are processed through the finishing process, they are called smooth spangle.
